The hand levels of the prior art are generally elongated, rectangular-shaped tools having peepholes through which vials containing liquid may be viewed. When placed on a surface parallel to a horizontal or vertical plane, the indicators in these vials can be read to determine whether the plane is perfectly horizontal or vertical, as the case may be.
Levels are of particular value on construction sites and tend to be used repeatedly and in different locations throughout an individual site. They therefore need to be easily portable.
However, construction sites are also often exposed to the elements. Wind or rain could cause displacement of a very lightweight tool. A hand level should therefore have sufficient weight so that the level remains where placed both when in and when not in use.
Because portability is desirable in a tool of this type, a level should be easy to grasp and carry. Since levels need to be elongated to properly measure pitch, such a tool can be awkward to carry. Consequently, a level should be constructed in a manner that makes it relatively easy to grasp and carry by hand.
Some of the levels of the prior art incorporate sides that are concave or are otherwise not perpendicular to each other. For example, U.S. Pat. No. 285,775 (Youngs) has a generally concave surface along each of two opposed wider sides, with a flat central portion between two curved edge portions. The level of the Youngs patent has a glass bulb and brass ring protruding from one of the concave sides, making it unsymmetrical along its length. This level also incorporates substantial open areas along its length.
U.S. Pat. No. 377,870 describes a level having concave sides. However, the concavity of the Youngs' and St. John's designs are not intended to, nor do they, facilitate grasping the device in either case.
These and other known devices of the prior art have certain disadvantages. For example, these prior inventions are not as easy to grasp and carry as the present invention. Furthermore, these prior inventions do not adequately protect the viewing portion of the levels from possible marring or scratching.
Another disadvantage of the prior art is a lack of symmetry, making the devices of the prior art less stable when placed on a surface for use or storage. Such a lack of symmetry makes such devices more likely to fall over unexpectedly, resulting in inefficiency, possible incorrect readings, or damage to the device.